Holographic storage medium comprising polyfunctional epoxy monomers capable of undergoing cationic polymerization

ABSTRACT

Disclosed is a holographic recording medium. The novel holographic recording mediums disclosed herein comprises: a) at least one polyfunctional epoxide monomer or oligomer which undergoes acid initiated cationic polymerization. Each epoxide in the monomer or oligomer is linked by group comprising a siloxane to a silicon atom and each monomer or oligomer has an epoxy equivalent weight of greater than about 300 grams/mole epoxide; b) a binder which is capable of supporting cationic polymerization; c) an acid generator capable of producing an acid upon exposure to actinic radiation; and optionally d) a sensitizer.

RELATED APPLICATION

[0001] This application is a divisional of U.S. application Ser. No.09/941,166, filed Aug. 28, 2001, which claims the benefit of U.S.Provisional Application No. 60/228,121, filed on Aug. 28, 2000. Theentire teachings of the above applications are incorporated herein byreference.

GOVERNMENT FUNDING

[0002] The invention was supported, in whole or in part, by grantMDA972-94-2-0008 from the Defense Advanced Research Projects Agency. Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0003] This invention relates to a holographic recording medium and tothe composition of this medium which provides for a condition of lowvolume shrinkage, good recording sensitivity, and high dynamic range.

[0004] In prior art processes for formation of volume-phase holograms,data is stored as holograms resulting from the interference of signaland reference beams within a holographic recording medium comprising ahomogenous mixture of at least one polymerizable monomer or oligomer anda polymeric binder; the polymerizable monomer or oligomer must of coursebe sensitive or sensitized to the radiation used to form theinterference fringes. In the illuminated regions of the interferencepattern, the monomer or oligomer undergoes polymerization to form apolymer that has a refractive index different from that of the binder.Diffusion of the monomer or oligomer into the illuminated regions, withconsequent chemical segregation of binder from these areas andalteration in its concentration in the non-illuminated regions, producesspatial separation between the polymer formed from the monomer oroligomer and the binder, thereby providing the refractive indexmodulation needed to form a hologram. Typically, after the holographicexposure, a post-imaging blanket exposure of the medium to actinicradiation is required to complete the polymerization of the monomer oroligomer and fix the hologram. When holograms are multiplexedco-locationally, such as by multiple holographic exposures at differentangle conditions, a post-imaging blanket exposure of the medium toactinic radiation may also be required to complete the polymerization ofthe monomer or oligomer and fix the multiplexed holograms.

[0005] One important potential use of volume holograms is in digitaldata storage; the three dimensional nature of a volume hologram, whichrefers to the storage of each bit as a hologram extending throughout theentire volume of the recording medium, renders volume holograms suitablefor use in high capacity digital data storage. A group of bits can beencoded and decoded together as a two dimensional array of bits referredto as a page. Various multiplexing methods, such as angular,spatioangular, shift, wavelength, phase-code, and related methods, areused to store multiple pages co-locationally within the same volume orin partially overlapping volumes.

[0006] Photopolymerizable holographic recording media forwrite-once-read-many (WORM) data storage applications should ideallyexhibit pre-recording shelf life of at least a year, good recordingsensitivity, high degree of optical homogeneity (i.e. low scattering),uniform recording characteristics, stable image fidelity, and low volumeshrinkage coupled with high dynamic range or cumulative gratingstrength. Low volume shrinkage coupled with good dynamic range andrecording sensitivity, however, remains as one of the most difficult toachieve performance characteristics for photopolymerizable holographicrecording media that are designed for data storage applications.Typically, high dynamic range is achievable with photopolymer recordingmaterials but the resultant volume shrinkage is significant and thuspoor image fidelity and poor signal to noise results. Uh-Sock Rhee etal. in Applied Optics, 34, 5, 846 (1995) describe the shrinkage effectin Dupont HRF-150-38 photopolymer as a function of increasing exposure.This material comprises monomers that are photopolymerized usingconventional free radical polymerization chemistry. The magnitude of thedeviation of the Bragg angle, displayed in FIGS. 6 and 7 of the abovereference, is about 2.5° This value is five times larger than the fullwidth at half maximum (FWHM) of the Bragg peak for a plane-wave hologramwith a grating period in the intermediate range of a digital page basedimage, and which is recorded in a medium thickness of only 100 μm.Accordingly, even for such a thin recording medium, which is notsufficiently thick for a holographic data storage medium, the angleshift from the recording condition exhibited by the Dupont HRF-150-38material is so large that no diffraction efficiency is observed at therecording angle condition, and thus an image could not be reconstructedwithout substantially tuning the angle of the read beam. Tuning theangle of the read beam is not desirable for a holographic data storagesystem since this imposes significant overhead on the readout design andwould seriously impair data rates. Furthermore, a single tuningadjustment would be inadequate to read an image affected by such levelsof shrinkage, since page based images comprise a continuum of plane-wavegrating components with a range of grating angles. Contributions to animage from larger grating angle components would be shifted further inangle from the Bragg condition than for smaller grating anglecomponents, and thus differential tuning would be required toreconstruct the high and low frequency features of an image. For thickerrecording media this problem is exacerbated further due to the inverseproportionality of FWHM on media thickness.

[0007] A consequence of high volume shrinkage is the requirement to useup a portion of the reactive monomeric or oligomeric species in therecording medium before holographic recording of information can beimplemented with reasonable fidelity. This step has the effect ofdiminishing the usable dynamic range as well as causing significantdecline in recording sensitivity. An example of this tradeoff is thephotopolymer material developed by Lucent Technologies, and which isbased upon conventional free radical polymerization chemistry. By way ofexample, this material comprises difunctional acrylate oligomers andmonomers such as N-vinyl carbazole and isobornyl acrylate (see Dhar etal. in Optics Letters, 23, 21, 1710 (1998), all of which exhibitsignificant volume shrinkage upon polymerization. Accordingly, Dhar etal. describe that if more than twenty 480-kbit images are recordedco-locationally in this material, for either 250 or 500 μm thick media,then the raw bit-error rate (BER) rises above the desired upper limitvalue of 5e-3. This occurs due to excessive volume shrinkage, whichfirstly reduces image fidelity and secondly causes an increased degreeof Bragg detuning as the extent of polymerization increases. In OpticsLetters, 24, 7, 487 (1999), Dhar et al. describe a photopolymerrecording media that exhibits moderate dynamic range per unit thicknessbut which suffers from significant volume shrinkage. Accordingly, Dharet al. show that the cumulative grating strength for a material thatexhibits 0.5% transverse shrinkage declines by a factor of about 4 to 5when the concentration of monomer is reduced in order to achieve animproved and minimally desirable value of 0.2% transverse shrinkage.Consequently, for 200 μm thick media Dhar describes that the cumulativegrating strength diminishes from about 9 to about 2, an unacceptably lowvalue, when a preconditioning step is used to consume a portion of themonomeric species in order to reduce shrinkage during holographicrecording. Additionally, the recording sensitivity of the recordingmaterial declines when the monomer concentration is reduced tocompensate for shrinkage, as the physical state of the material duringrecording more closely resembles a glassy polymer in which diffusionrates are substantially reduced.

[0008] Accordingly, despite Dhar et al. having prepared such materialswith increased thicknesses, up to about 1 mm, in order to compensate forthe serious decrease in dynamic range exhibited at acceptable levels oftransverse shrinkage, the recording sensitivity was still low. Whenholographic recording media are prepared with increased media thickness,however, then the degree of Bragg detuning, exhibited for any givenlevel of transverse shrinkage, becomes more problematic as a result ofthe concomitant diminution in the peak width of the Bragg selectivityangular profile. In particular, when the magnitude of Bragg detuning islarge relative to the Bragg selectivity peak width, then the observeddiffraction efficiency is substantially lower than the value at theBragg peak, and thus the raw BER of a reconstructed image increasessignificantly as a result of decreased signal to noise ratio.

[0009] In prior art, holographic recording media based upon cationicring opening polymerization have employed monomers which whenhomopolymerized produce hard and brittle polymers due to high crosslinkdensity. High crosslink density can act to inhibit attainment ofsignificant extents of polymerization reaction. This is particularly thecase for multifunctional moieties where enthalpy values forhomopolymerizations can be less than about 50 (kJ/mole epoxide).Previous compositions comprising such multifunctional monomers aredescribed by way of example in U.S. Pat. No. 5,759,721 and in U.S.patent application No. 08-970,066. Although these monomers exhibitconsiderably reduced shrinkage upon polymerization, as compared to othermonomers such as acrylates, the remaining shrinkage coupled with theirrelatively unyielding mechanical properties can cause both mechanicaland optical difficulties when employed in holographic recording mediawith thickness of 200 μm or greater. Additionally, inhibition ofsignificant extents of polymerization reaction due to high crosslinkdensity prevents attainment of the full dynamic range of thephotopolymerizable medium during holographic recording.

SUMMARY OF THE INVENTION

[0010] It has now been found that multifunctional epoxide monomers withan epoxy equivalent weight greater than 300 grams per mole of epoxideare suitable for use in holographic recording materials. It has alsobeen found that holographic recording materials comprising certain ofthese multifunctional epoxide monomers exhibit significantly decreasedshrinkage, cracking and brittleness compared with the holographicrecording materials of the prior art (Examples 6 and 7). Based on thesediscoveries, novel multifunctional epoxide monomers, novel holographicrecording materials and methods of preparing these novel holographicrecording materials are disclosed herein.

[0011] One embodiment of the present invention is a holographicrecording medium comprising a binder capable of supporting cationicpolymerization, an acid generator capable of producing an acid uponexposure to actinic radiation, and a multifunctional epoxide monomercapable of undergoing cationic polymerization and which has an epoxyequivalent weight greater than about 300 (grams/mole epoxide). Asdiscussed below, certain acid generators also require sensitizers.Preferably, the holographic recording medium additionally comprises adifunctional and/or a monofunctional epoxide monomer capable ofundergoing cationic polymerization. Optionally, the monofunctional anddifunctional monomer have an epoxy equivalent weight less than about 225(grams/mole epoxide). The holographic medium of the present invention ispreferably essentially free from materials capable of undergoing freeradical polymerization.

[0012] Another embodiment of the present invention is a multifunctionalepoxide monomer that undergoes acid initiated cationic polymerization.Each epoxide in the monomer is linked by a group comprising a siloxaneto a central silicon atom or alternatively in linked to a centralpolysiloxane ring, and each monomer and oligomer has an epoxy equivalentweight of greater than about 300 grams/mole epoxide and preferably lessthan about 1000 grams/mole epoxide. More preferably, the monomer has anepoxy equivalent weight between about 300 and about 700 grams/moleepoxide.

[0013] Another embodiment of the present invention is a mixturecomprising a binder capable of supporting cationic polymerization and amultifunctional epoxide monomer capable of undergoing cationicpolymerization and which has an epoxy equivalent weight greater thanabout 300 grams/mole epoxide. Preferably, the mixture additionallycomprises a difunctional and/or monofunctional epoxide monomer capableof undergoing cationic polymerization and which preferably have an epoxyequivalent weight less than about 225 (grams/mole epoxide). This mixturecan be used in the preparation of the holographic recording materials ofthe present invention by adding thereto the other components of themedium, as described below.

[0014] Yet another embodiment of the present invention is a method ofpreparing the holographic recording medium of the present invention. Themethod comprises the step of combining the binder, and multifunctionalepoxide monomer(s) having an epoxy equivalent weight greater than about300 grams/mole epoxide and the acid generator. When present, thesensitizer and the difunctional and/or multifunctional epoxide monomerare also combined therewith. Preferably, the binder and multifunctionalepoxide monomer having an epoxy equivalent weight greater than about 300grams/mole epoxide and, when present, the monofunctional anddifunctional monomers are combined before adding the other components.

[0015] The large epoxy equivalent weight of the multifunctional epoxidemonomers used in the holographic recording materials disclosed hereinreduces crosslink density, and accordingly a greater extent ofpolymerization reaction can be achieved during exposure to actinicradiation. Consequently, increased dynamic range can be attained duringholographic recording. In addition, holographic recording materialscomprising a number of the disclosed multifunctional epoxide monomersexhibit significantly decreased shrinkage, cracking and brittlenesscompared with the holographic recording materials of the prior art. Themonomers and oligomers described here have the advantage of beingcompatible with the preferred siloxane binders and of exhibitingenthalpy values for homopolymerization that can exceed 75 (kJ/moleepoxide).

DETAILED DESCRIPTION OF THE INVENTION

[0016] Suitable monomers and oligomers for use in the present inventionare stable on prolonged storage but capable of undergoing rapid cationicpolymerization. They are also miscible with binders used for holographicrecording materials. Typically, the monomers and oligomers are siloxaneswith epoxy functional groups. The preferred type of epoxy group is acycloalkene oxide group, especially a cyclohexene oxide group. A“polyfunctional” monomer or oligomer is a compound having at least threegroups of the specified functionality, in the present case at leastthree epoxy groups. The terms “polyfunctional” and “multifunctional” areused interchangeably herein. A “difunctional” monomer or oligomer is acompound having two groups of the specified functionality; and a“monofunctional” monomer or oligomer is a compound having one group ofthe specified functionality.

[0017] Polyfunctional monomers of the present invention typically havethree or four epoxides (preferably cyclohexene oxide) groupingsconnected by a linker through an Si—O group, i.e., a “siloxane group”,to a central Si atom. Alternatively, the epoxides are connected by alinker to a central polysiloxane ring. For example, certain polymers andoligomers are represented by Structural Formula (I):

R″—Si—R′₃   (I).

[0018] Each R′ in Structural Formula (I) is independently an epoxidesubstituted aliphatic group connected by an inert linker groupcomprising a siloxane to the central silicon atom. In one example, R′comprises a group represented by Structural Formula (II):

[0019] X₁ and X₂ are independently an inert linking group. Preferably X₂is —O—.

[0020] Each R^(a) is independently a substituted or unsubstitutedaliphatic group or a substituted or unsubstituted aryl group.

[0021] Each R^(b) is an aliphatic group substituted with an epoxide.

[0022] R″ in structural Formula (I) is R′ or —H, a substituted aliphaticgroup, an unsubstituted aliphatic group, a substituted aryl group, anunsubstituted aryl group, a substituted siloxane group, an unsubstitutedsiloxane group, a substituted polysiloxane group or an unsubstitutedpolysiloxane group.

[0023] In one preferred embodiment, the polyfunctional monomer isrepresented by Structural Formula (III):

[0024] n is 1, 2, 3 or 4; and R is a substituted or unsubstitutedaliphatic group, a substituted or unsubstituted aryl group or is a grouprepresented by Structural Formula (IV) or (V):

[0025] Each R^(a), R^(b) X₁ and X₂ is as defined above in StructuralFormula (II); R^(c) is H, an unsubstituted aliphatic group, asubstituted aliphatic group, an unsubstituted aryl group, a substitutedaryl group, a substituted siloxane group, an unsubstituted siloxanegroup, a substituted polysiloxane group or an unsubstituted polysiloxanegroup.

[0026] One example of a polyfunctional monomer represented by StructuralFormula (III) is a monomer represented by Structural Formula (VI):

[0027] R in Structural Formula (VI) is a group represented by StructuralFormula (VII) or (VIII).

[0028] Each group R¹, each group R³ and each group R⁴ is independently asubstituted or unsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, arylsubstituted C₁₋₁₂ alkyl or aryl group.

[0029] Each group R² is independently a substituted or unsubstitutedC₁₋₁₂ alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylenegroup, —Y₁—[O—Y₁]_(p)—, —Y₁—Si(R^(z))₂—Y₁—,—Y₁—Si(R^(z))₂—Y₁—O—Y₁—Si(R^(z))₂—Y₁—, or—Y₁—Si(R^(z))₂—Y₁—Si(R^(z))₂—Y₁—.

[0030] Each R⁵ is, independently, an epoxide substituted aliphatic grouphaving 2-10 carbon atoms.

[0031] Each group R⁶ is independently hydrogen, an alkenyl, asubstituted or unsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, arylsubstituted C₁₋₁₂-alkyl or aryl or R^(z)—(O—Y₁)_(m)—,(R^(z))₃Si—(O—Si(R^(z))₂)_(q)—Y₁— or (R^(z))₃Si—(O—Si(R^(z))₂)_(q)—O—.

[0032] Each R^(z) is independently a substituted or unsubstituted C₁₋₁₂alkyl group, C₁₋₁₂ cycloalkyl alkyl group, aryl substituted C₁₋₁₂ alkylgroup or aryl group.

[0033] Each Y₁ is independently a C₁₋₁₂ alkylene group.

[0034] p is an integer from 1 to 5 (preferably 1); m is an integer from1-10 (preferably 1); and q is an integer from 0 to 4 (preferably 0 or1).

[0035] Preferably, R² is independently a substituted or unsubstitutedC¹⁻¹² alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylenegroup; and each R⁶ is independently a substituted or unsubstituted C₁₋₁₂alkylsilane, C₁₋₁₂ cycloalkylsilane, C₁₋₁₂ alkoxysilane, arylsubstituted C₁₋₁₂ alkylsilane, a hydrogen, a vinyl, a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ dialkylether (alkyl-O-alkylene-),(C₁₋₁₂ cycloalkyl)C₁₋₁₂ alkylether (cycloalkyl-O-alkylene-), C₁₋₁₂cycloalkyl, aryl substituted C₁₋₁₂ alkyl or aryl group.

[0036] Specific monomers of this type are those in which R is a grouprepresented by Structural Formula (VII) or (VIII) and wherein each groupR¹, each group R³ and each group R⁴ is a methyl group; each group R² isan ethylene, hexylene, or octylene group; each group R⁵ is a2-(3,4-epoxycyclohexyl) ethyl grouping, and each group R⁶ is a hydrogenor ethenyl (—CH═CH₂).

[0037] Another example of a polyfunctional monomer represented byStructural Formula (III) is a monomer represented by Structural Formula(IX):

[0038] R¹⁴ is represented by Structural Formula (X) or (XI):

[0039] Each group R¹⁵, each group R¹⁷, each group R¹⁸, each group R¹⁹,each group R²⁰ and each group R²² is independently a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substituted C₁₋₁₂alkyl or aryl group.

[0040] R¹⁶ is independently a substituted or unsubstituted C₁₋₁₂alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylene group,—Y₁—[O—Y₁]_(p)—, —Y₁—Si(R^(z)) ₂—Y₁—,—Y₁—Si(R^(z))₂—Y₁—O—Y₁Si(R^(z))₂—Y₁—, or—Y₁—Si(R^(z))₂—Y₁—Si(R^(z))₂—Y₁—.

[0041] Each R²¹ is independently an epoxide substituted aliphatic grouphaving 2-10 carbon atoms.

[0042] R²³ is independently hydrogen, an alkenyl, a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substitutedC₁₋₁₂-alkyl or aryl or R^(z)—(O—Y₁)_(m)—,(R^(z))₃Si——(O—Si(R^(z))₂)_(q)—Y₁— or (R^(z))₃Si—(O—Si(R^(z))₂)_(q)—O—.

[0043] Each group X is independently oxygen or R¹⁶.

[0044] R^(z), Y₁, m, p and q are as described above.

[0045] Preferably, R¹⁶ is independently a substituted or unsubstitutedC₁₋₁₂ alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylenegroup; X is —O—; and each group R²³ is independently a hydrogen, amonovalent substituted or unsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ dialkylether(alkyl-O-alkylene-), C₁₋₁₂ cycloalkyl C₁₋₁₂ alkylether(cycloalkyl-O-alkylene-), C₁₋₁₂ cycloalkyl, aryl substituted C₁₋₁₂ alkylor aryl group.

[0046] Examples of specific monomers represented by Structural Formula(IX) are those in which X is —O—; R¹⁴ is represented by StructuralFormulas (X) and (XI); each group R¹⁵, R¹⁷, R¹⁸ R¹⁹, R²⁰ and R²² is amethyl group; each group R¹⁶ is an ethylene, hexylene, or octylenegroup; each group R²¹ is a 2-(3,4-epoxycyclohexyl) ethyl grouping; andR²³ is a hydrogen, hexyl, or alkylether.

[0047] In a second preferred embodiment, the polyfunctional monomer isrepresented by Structural Formula (XII):

[0048] Each group R⁷ is independently an unsubstituted aliphatic group,a substituted aliphatic group, an unsubstituted aryl group or asubstituted aryl group.

[0049] Each group R⁸ is R⁹, hydrogen, an alkenyl, a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substitutedC₁₋₁₂-alkyl or aryl or R^(z)—(O—Y₁)_(m)—,(R^(z))₃Si——(O—Si(R^(z))₂)_(q)—Y₁— or (R^(z))₃Si—(O—Si(R^(z))₂)_(q)—O—.

[0050] Each R⁹ is independently represented by Structural Formula (II).

[0051] R^(z), Y₁, q and m are as defined above.

[0052] In one example of a compound represented by Structural Formula(XII), R⁷—R¹³ are defined below.

[0053] Each group R⁷ is independently a substituted or unsubstitutedC₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substituted C₁₋₁₂ alkyl or arylgroup.

[0054] R⁸ is a defined above. Preferably, R⁸ is R⁹ or a substituted orunsubstituted C₁₋₁₂ alkylsilane, C₁₋₁₂ cycloalkylsilane, C₁₋₁₂alkoxysilane, arylsubstituted C₁₋₁₂ alkyl silane or a substituted orunsubstituted 1-alkenyl group or a substituted or unsubstituted C₁₋₁₂n-alkenyl group where n is greater than or equal to 1.

[0055] R⁹ is represented by Structural Formula (XIII):

[0056] Each group R¹⁰ is independently a substituted or unsubstitutedC₁₋₁₂ alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylenegroup, —Y₁—[O—Y₁]_(p)—, —Y₁—Si(R^(z))₂—Y₁—, —Y₁—Si(R^(z))₂—Y₁—O—Y₁—Si(R^(z))₂—Y₁—, or —Y₁—Si(R^(z))₂—Y₁—Si(R^(z))₂—Y₁—. Preferably, eachgroup R¹⁰ is independently a substituted or unsubstituted C₁₋₁₂alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylene group.

[0057] Each R^(z), Y₁ and p is as defined above.

[0058] Each group R¹¹ and R¹² is independently a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substituted C₁₋₁₂alkyl group or aryl group.

[0059] Each group R¹³ is independently an epoxide substituted aliphaticgroup having from 2-10 carbon atoms.

[0060] Specific examples of monomers represented by Structural Formula(XII) include those in which each R⁷, each R¹¹ and each R¹² is a methylgroup; R⁸ is ethenyl (—CH═CH₂) or a R⁹; R⁹ is represented by StructuralFormula (XIII); each group R¹⁰ is an —(CH₂)₂—, —(CH₂)₆— or —(CH₂)₈—; andeach group R¹³ is a 2-(3,4-epoxycyclohexyl) ethyl group.

[0061] One example of a difunctional epoxide monomer suitable for use inthe disclosed holographic recording materials is a compound representedby Structural Formula (XIV):

[0062] R¹ and R⁵ are as defined above. Compounds of this type arecommercially available from Polyset Corporation, Inc., Mechanicsville,N.Y.

[0063] Examples of suitable monofunctional epoxide monomers arerepresented by Structural Formula (XIVa):

[0064] An “inert linking group” is a moiety which: 1) does not reactunder conditions which induce or initiate cationic polymerization ofepoxides; does not interfere with acid initiated cationic polymerizationof epoxides; 3) and does not interfere with chemical segregation ofbinder from polymer formed during cationic polymerization of epoxides.An alkylene group (substituted or unsubstituted), i.e., —(CH₂)_(n)—,wherein n is a positive integer, preferably from 1-12, an arylene group(substituted or unsubstituted) and —O—are examples of an inert linkinggroup. The term “arylene” refers to an aryl group which is connected tothe remainder of the molecule by two other bonds. By way of example, thestructure of a 1,4-phenylene group is shown below:

[0065] Others examples of suitable inert linking groups include(substituted or unsubstituted) an alkylene group (preferably C₁₋₁₂) inwhich one or more methylene groups are replaced with a cycloalkyl group(a “cycloalkylene group”), an aryl group (an “arylalkylene group”), —O—or —Si(R^(y))₂—, wherein —R^(y) is as defined above. Specific examplesinclude —Y¹—[O—Y]_(p)—, —Y₁—Si(R^(z))₂—Y₁—,—Y—Si(R^(z))₂—Y₁—O—Y₁—Si(R^(z))₂—Y₁—, or—Y₁—Si(R^(z))₂—Y₁—Si(R^(z))₂—Y₁—; and Y₁, R^(z) and p are as definedabove.

[0066] An “alkylsilane group” can be represented by (R^(z))₃Si—Y₁—,wherein R^(z) and Y₁ are as defined above, provided that at least oneR^(z) is alkyl; a “cycloalkylsilane group” can be represented by(R^(z))₃Si—Y₁—, wherein R^(z) and Y¹ are as defined above, provided thatat least one R^(z) is cycloalkyl; an “alkoxysilane group” can berepresented by (R^(z−)O—)₃Si—Y₁—, wherein R^(z) and Y₁ are as definedabove, provided that at least one R^(z) is alkyl; and an “arylsubstituted alkylsilane group” can be represented by (R^(z))₃Si—Y₁—,wherein R^(z) and Y₁ are as defined above, provided that at least oneR^(z) is an aryl substituted alkyl group.

[0067] A “siloxane group” can be represented by (R^(z))₃SiO—, whereinR^(z) is as defined above. When at least one alkyl or aryl grouprepresented by R^(z) is substituted, the siloxane group is said to besubstituted. A “polysiloxane group” can be represented by(R^(z))₃Si—(O—Si(R^(z))₂)_(q)—O—, wherein R^(z) is as defined above andq is an integer, preferably from 1 to 4. When at least one alkyl or arylgroup represented by R^(z) is substituted, the polysiloxane group issaid to be substituted.

[0068] A “dialkyl ether” can be represented by R—O—Y₁—, wherein R is analkyl group and Y₁ is an alkylene group; and a “cycloalkylalkyl ether”can be represented by R—O—Y₁—, wherein R is a cycloalkyl group and Y₁ isan alkylene group.

[0069] An aliphatic group is a straight chained, branched or cyclicnon-aromatic hydrocarbon which is completely saturated or which containsone or more units of unsaturation. Typically, a straight chained orbranched aliphatic group has from 1 to about 12 carbon atoms, preferablyfrom 1 to about 8, and a cyclic aliphatic group has from 3 to about 10carbon atoms, preferably from 3 to about 8. An aliphatic group ispreferably a straight chained or branched alkyl group, e.g, methyl,ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, pentyl,hexyl, heptyl or octyl, or a cycloalkyl group with 3 to about 8 carbonatoms. A C₁₋₁₂ straight chained or branched alkyl group or a C₃₋₈ cyclicalkyl group is also referred to as a “lower alkyl” group. An aliphaticgroup with one unit of unsaturation is referred to an “alkenyl” group.

[0070] Suitable aryl groups groups for momomers of the present inventionare those which 1) do not react under conditions which induce orinitiate cationic polymerization of epoxides; 2) do not interfere withacid initiated cationic polymerization of epoxides; 3) and do notinterfere with chemical segregation of binder from polymer formed duringcationic polymerization of epoxides. Examples include, but are notlimited to, carbocyclic aromatic groups such as phenyl, naphthyl andbiphenyl.

[0071] Suitable substituents on an aliphatic group (including analkylene or alkenyl group) or an aryl group carbocyclic and heteroaryl)are those which 1) do not react under conditions which induce orinitiate cationic polymerization of epoxides; 2) do not interfere withacid initiated cationic polymerization of epoxides; 3) and do notinterfere with separation of binder from polymer formed during cationicpolymerization of epoxides unless the group comprises an epoxide moiety.Examples of suitable substituents include, but are not limited to,halogens, R₃Si—, alkyl groups, aryl groups and —OR. Each R isindependently a substituted or unsubstituted aliphatic group or asubstituted or unsubstituted aryl group, preferably an alkyl group or anaryl group.

[0072] The binder used in the process and preparation of the presentmedium should, of course, be chosen such that it does not inhibitcationic polymerization of the monomers used (e.g., “supports” cationicpolymerization), such that it is miscible with the monomers used and thepolymerized structure obtained from such monomers, and such that itsrefractive index is significantly different from that of the polymerizedmonomer or oligomer (e.g., the refractive index of the binder differsfrom the refractive index of the polymerized monomer by at least 0.04and preferably at least 0.09). Binders can be inert to thepolymerization processes described herein or optionally can polymerizeduring one or more of the polymerization events.

[0073] Preferred binders for use in the current process arepolysiloxanes, due in part to availability of a wide variety ofpolysiloxanes and the well documented properties of these oligomers andpolymers. The physical, optical, and chemical properties of thepolysiloxane binder can all be adjusted for optimum performance in therecording medium inclusive of, for example, dynamic range, recordingsensitivity, image fidelity, level of light scattering, and datalifetime. The efficiency of the holograms produced by the presentprocess in the present medium is markedly dependent upon the particularbinder employed. Although those skilled in the holographic art will haveno difficulty in selecting an appropriate binder by routine empiricaltests, in general it may be stated that poly(methyl phenyl siloxanes)and oligomers thereof, such as1,3,5-trimethyl-1,1,3,5,5-pentaphenyltrisiloxane. Examples are sold byDow Corning Corporation under the tradename DOW Coming 705 (a trimer)and DOW Coming 710 and have been found to give efficient holograms.

[0074] The acid generator used in the recording medium of the presentinvention produces an acid upon exposure to the actinic radiation. Theterm “acid generator” or PAG is used herein to refer to the component orcomponents of the medium that are responsible for the radiation-inducedformation of acid. Thus, the acid generator may comprise only a singlecompound that produces acid directly. Alternatively, the acid generatormay comprise an acid generating component which generates acid and oneor more sensitizers which render the acid generating component sensitiveto a particular wavelength of actinic radiation, as discussed in moredetail below. The acid produced from the acid generator may be either aBronstead acid or Lewis acid, provided of course that the acid is of atype and strength which will induce cationic polymerization of themonomer. When the acid produces a Bronstead acid, this acid preferablyhas a pK_(a) less than about 0. Known superacid precursors such asdiazonium, sulfonium, phosphonium and iodonium salts may be used in thepresent medium, but iodonium salts are generally preferred.Diaryliodonium salts have been found to perform well in the presentmedia, with specific preferred diaryliodonium salts being(5-octyloxyphenyl)phenyliodonium hexafluoroantimonate andditolyliodonium tetrakis(pentafluorophenyl)borate, diphenyliodoniumtetrakis(pentafluorophenyl)borate, tolylphenyliodoniumtetrakis(pentafluorophenyl)borate and cumyltolyliodoniumtetrakis(pentafluorophenyl)borate.

[0075] In the absence of any sensitizer, iodonium salts are typicallyonly sensitive to radiation in the far ultra-violet region, below about300 nm, and the use of far ultra-violet radiation is inconvenient forthe production of holograms because for a given level of performanceultra-violet lasers are substantially more expensive than visiblelasers. It is well known, however, that by the addition of varioussensitizers, iodonium salts can be made sensitive to various wavelengthsof actinic radiation to which the salts are not substantially sensitivein the absence of the sensitizer. Such sensitizers include, by way ofexample, Rubrene. In addition, iodonium salts can be sensitized tovisible radiation using certain aromatic hydrocarbons substituted withat least two alkynyl groups or two alkenyl groups, a specific preferredsensitizer of this type being 5,12-bis(phenylethynyl)naphthacene. Thissensitizer renders iodonium salts sensitive to the 514.5 nm radiationfrom an argon ion laser, and to the 532 nm radiation from afrequency-doubled YAG laser, both of which are convenient sources forthe production of holograms. Preferably, the sensitizer isphotobleachable so that the visible absorption of the holographic mediumdecreases during exposure.

[0076] The proportions of acid generator, sensitizer, binder andmonomers in the holographic recording medium of the present inventionmay vary rather widely, and the optimum proportions for specificcomponents and methods of use can readily be determined empirically byskilled workers. Guidance in selecting suitable proportions is providedin U.S. Pat. No. 5,759,721, the teachings of which are incorporatedherein by reference. In general, however, it is preferred that thepresent medium comprise from about 0.25 to about 5 parts by weight ofthe monofunctional or difunctional epoxide per part by weight of thepolyfunctional epoxide monomer which has an epoxy equivalent weightgreater than about 300 (g/mole epoxide). The solution of monomers withbinder can comprise a wide range of compositional ratios, preferablyranging from about 90 parts binder and 10 parts monomer or oligomer(w/w) to about 10 parts binder and 90 parts monomer or oligomer (w/w).It is preferred that the medium comprise from about 0.167 to about 5parts by weight of the binder per total weight of the monomers.Typically, the medium comprises between about 0.005% and about 0.5% byweight sensitizer, when present, and between about 1.0% and about 10.0%by weight acid generator.

[0077] Syntheses of the polyfunctional monomers of the present inventionare shown in Schemes 1-5. These syntheses are based on a hydrosilylationin which an olefin is reacted with a silane in the presence of asuitable metal catalyst, such as the Karstedt catalyst (see U.S. Pat.No. 3,715,334), tetrakis(triphenylphosphine)platinum(0), or Wilkinson'scatalyst (RhCl(Ph₃P)₃). In particular, the syntheses selectively react asingle silane group (—Si—H) in a compound comprising two more suchgroups. Selective hydrosilyation reactions of this type are described,for example, in U.S. Pat. No. 5,484,950, Crivello et al., PolymerPreprints 32.173 (1991), Crivello et al., J. Macromolecular Science—Pureand Applied Chemistry A31 :1001 (1994) and Crivello and Bi, PolymerScience 32:683 (1994), the entire teachings of which are incorporatedherein by reference.

[0078] In Scheme 1, one silane group of tetramethyldisiloxane (XV) isreacted with an epoxide substituted aliphatic olefin such as thecompound represented by structural formula (XVI). The product,represented by Structural Formula (XVII), can then undergo a secondhydrosilylation reaction with tetrakis(vinyldimethylsiloxy)silane,represented by Structural Formula (XVIII), to form the productrepresented by Structural Formula (XIX). It is noted that this productis encompassed within Structural Formula (VI). Specific conditions forcarrying out these reactions are provided in Example 1.

[0079] Polyfunctional epoxide monomers with longer chains can beprepared according to Scheme 2, which utilizes an additionalhydrosilylation reaction. Specifically, compound (XVII) ishydrosilylated with a diolefin, preferably with an excess of thediolefin. The product, represented by Structural Formula (XX), thenundergoes a second hydrosilylation with tetrakis(dimethylsiloxy)silane,represented by Structural Formula (XXI). The final product, representedby Structural Formula (XXII), is encompassed within Structural Formula(III). R² in Scheme 2 is —(CH₂)_(n+4)—. Specific conditions for thesereactions are provided in Example 2.

[0080] Further chain elongations are possible, as shown in Scheme 3. Theintermediate represented by Structural Formula (XX) is hydrosilylatedwith 1,1,3,3-tetramethyldisiloxane (XXIII) to form a product representedby Structural Formula (XXIV), which is then used to hydrosilylatetetrakis(vinyldimethylsiloxy)silane to form a product represented byStructural Formula (XXV). This final product is encompassed withinStructural Formula (IX). R¹⁶ in Scheme 3 is —(CH₂)_(n+4)—; and R16A is—(CH₂)₂—.

[0081] In Scheme 4,1-[2-(3{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane (XVII)is reacted with 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane(XXVI) to form the product XXVII, which is encompassed within StructuralFormula (XII). Specific conditions for this reaction are provided inExample 3.

[0082] Scheme 5 shows the same synthesis as Scheme 3, except that1,3-divinyltetramethyldisiloxane is used in place of an aliphatic diene.The product represented by Structural Formula (XXX), is encompassedwithin Structural Formula (IX). Specific conditions for carrying outthis transformation is provided in Examples 4-5.

[0083] The following examples are now given, though by way ofillustration only, to show details of particularly preferred reagents,conditions, and techniques used in referred media and processes of thepresent invention.

EXEMPLIFICATION EXAMPLE 1 Preparation of a Compound Represented byStructural Formula (XIX)

[0084]

[0085] Tetrakis(vinyldimethylsiloxy)silane (Gelest Inc., SIT7312.0)(81.34 g, 188 mmol) and toluene (25 ml) were charged to an oven driedpressure equalized addition funnel.1-[2-(3{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane (194.30g, 752 mmol) was added into an oven dried 1 liter three-necked flaskequipped with a magnetic stirrer, pressure equalized addition funnel,thermometer, and an air condenser with a top mounted inlet/outlet forsupply of inert gas. Toluene (50.0 ml) was added to the reaction vessel.The mixture was stirred under inert gas atmosphere and thentetrakis(triphenylphosphine)platinum(0) (1.50 mg dissolved in 1.50m1toluene) was added via a gas tight syringe at ambient temperature.Internal temperature was raised to 55° C. andtetrakis(vinyldimethylsiloxy)silane was added dropwise to the reactionvessel at 55° C. Addition was complete within 4 hours and 20 minutes.The contents were stirred for an additional 4 hours and an aliquot wastaken and analyzed by Thin Layer Chromatography (TLC). TLC analysisrevealed that the reaction for formation of tetramer was proceeding, butat a slow rate.

[0086] Tetrakis(triphenylphosphine)platinum(0) (0.5 mg) and1-[2-(3{7-oxabicyclo[4.1.0.]heptyl})ethyl]-tetramethyldisiloxane (1.02g, 3.0 mmol) was added additionally and the internal temperature wasraised to 65° C. The contents were stirred at this temperature for 17hours, and Infrared Spectroscopy (FTIR) analysis of the Si—H stretchingregion revealed no remaining Si—H. The reaction content was cooled toambient temperature and it was further diluted with 500 ml hexanes andtreated with charcoal. Charcoal was removed by filtration and volatileswere removed by rotatory evaporator. Tetrafunctional epoxy monomer wasthen stirred under high vacuum (50-75 millitorr) overnight to removeremaining residual volatiles, and then filtered under nitrogen using a1.0 micron syringe filter. Yield was 272 g, 98.7%.

[0087] The resulting tetrafunctional epoxy monomer was mixed with aniodonium salt photoacid generator (cumyltolyliodoniumtetrakis(pentafluorophenyl)borate) (5 wt %) and the uniform mixture wastested by Photo-Differential Scanning Calorimetry (PDSC) forphotochemical sensitivity. Development of exothermicity, obtained byPDSC, was extremely rapid after the onset of exposure to broad band Hgradiation at an irradiance level of 8.5 mW/cm². The peak positionoccurred at 0.119 minutes and the onset of exothermicity was at 0.052minutes. The calculated enthalpy of polymerization reaction was 77.32kJ/(mole epoxide equivalent). The procedure followed for thismeasurement has been described by Waldman et al. J. Imaging Sci.Technol. 41(5): 497-514 (1997).

EXAMPLE 2 Preparation of the Compound Represented by Structural Formula(XXII)

[0088]

[0089] Tetrakis(dimethylsiloxy)silane (4.6019 g, 0.014 mol) and toluene(12.0 ml) were charged into an oven-dried 250-ml three-necked flaskwhich was equipped with a magnetic stirrer, pressure equalized additionfunnel, thermometer, and a condenser topped by an argon inlet/outlet.The reaction mixture was kept at ambient temperature and Karstedtcatalyst (1.0 mg of Gelest Inc., SIP6831.1 soln.) in 1.0 ml toluene wasadded.1,1,3,3-Tetramethyl-1-oct-7-enyl-3-[2-(7-oxa-bicyclo[4.1.0]hept-3-yl)-ethyl]-disiloxane(20.65 g, 0.056 mol) synthesized according to literature methods(Crivello, et al., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.)32(3):173-4(1991), and Crivello, et al., J. Polym. Sci., Part A: Polym.Chem. 31(10):2563-2572 (1993), was charged into the addition funnel.Addition of1,1,3,3-tetramethyl-1-oct-7-enyl-3-[2-(7-oxa-bicyclo[4.1.0]hept-3-yl)-ethyl]-disiloxanewas carried out between 32-36° C. and was completed within one hour.Reaction progress was monitored using FTIR analysis of the Si—Hstretching mode until no changes in Si—H content were observed.Additional catalyst solution (1.5 mg) and1,1,3,3-Tetramethyl-1-oct-7-enyl-3-[2-(7-oxa-bicyclo[4.1.0]hept-3-yl)-ethyl]-disiloxane(0.5g) were added and contents were stirred at 40° C. until FTIRanalysis revealed that Si—H content was no longer discernable. Thereaction mixture was diluted with 100 ml hexanes and treated withcharcoal. Charcoal was removed via filtration and volatiles were removedby rotatory evaporator. The resulting product was kept under high vacuumfor 17 hours to remove residual volatiles. The tetrafunctional epoxymonomer was filtered through a 1.0 μm syringe filter under nitrogenenvironment. Yield was 24.86 g, or 98%.

[0090] Photo-Differential Scanning Calorimetry (PDSC) was performed asdescribed in Example 1. Development of exothermicity was extremely rapidafter the onset of exposure to broad band Hg radiation at an irradiancelevel of 8.5 mW/cm². The peak position occurred at 0.139 minutes and theonset of exothermicity was at 0.062 minutes. The epoxy equivalent weightof the tetrafunctional epoxy monomer was 450.9. The enthalpy value was79.92 kJ/mol epoxy equivalent.

EXAMPLE 3 Synthesis of the Compound Represented by Structural Formula(XXVII) (1378.7/344.7 g/mole epoxide)

[0091]

[0092] 1-[2-(3{7-Oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane(6.05 g, 23.4 mmol) was weighed into an oven dried 100 ml three-neckedround-bottomed flask equipped with a magnetic stirrer. The reactionflask was then equipped with an oven dried pressure equalized additionfunnel, thermometer, and an air condenser with a top mountedinlet/outlet for supply of inert gas. Toluene (10.0 ml) was added to thereaction vessel. The mixture was stirred under inert gas atmosphere andthen Karstedt catalyst (2.00 mg in 2.00 ml toluene solution; see Example2) was added via a gas tight syringe at ambient temperature. Internaltemperature was raised to 45° C.2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (1.994 g, 5.79mmol) was then added dropwise from the pressure equalized additionfunnel into the reaction vessel. Addition was complete within one hour.Contents were stirred at 45° C. for an additional 3 hours followed by anincrease in the internal temperature to 65° C. after having added 5.0 mladditional toluene. After 18 hours, additional Karstedt catalyst (0.5 mgadded to 0.5 ml toluene) was added, following the addition of1-[2-(3{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane (100 mg,0.39 mmol), to drive the reaction to completion. The reaction contentwas stirred at 65° C. for 6 hours, at which point the reaction wasdetermined to be completed by FTIR analysis. The reaction mixture wascooled to ambient temperature and was diluted with 50 ml hexanesfollowed by treatment with charcoal. Charcoal was removed via filtrationand volatiles were removed by rotatory evaporator. Tetrafunctional epoxymonomer was then stirred under high vacuum (50-75 millitorr) overnightto remove remaining residual volatiles. Yield was 7.026 g, 88%.

[0093] Photo-Differential Scanning Calorimetry (PDSC) was performed asdescribed in Example 1. Development of exothermicity was rapid after theonset of exposure to broad band Hg radiation. The peak position was at0.126 minutes and the onset of exothermicity was at 0.059 minutes. Thecalculated enthalpy of polymerization reaction was 59.80 kJ/(moleepoxide equivalent).

EXAMPLE 4 Synthesis of3-(2-{1,1,3,3-Tetramethyl-3-[2-(1,1,3,3-tetramethyl-3-vinyl-disiloxanyl)-ethyl]-disiloxanyl}-ethyl)-7-oxa-bicyclo[4.1.0]heptane

[0094]

[0095] 1,3-Divinyltetramethyldisiloxane (20.00 g, 107.3 mmol) wasweighed into an oven dried 100 ml three-necked round-bottomed flaskequipped with a magnetic stirrer. The reaction flask was then equippedwith an oven dried pressure equalized addition funnel, thermometer, andan air condenser with a top mounted inlet/outlet for supply of inertgas. Tetrakis(triphenylphosphine)platinum(0) (1.00 mg dissolved in 1.00ml toluene) was added via a gas tight syringe at ambient temperature.1-[2-(3{7-Oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane (13.87g=53.6 mmol) was charged into the addition funnel and added dropwiseinto the reaction vessel maintaining the internal temperature at 30-35°C. Addition was complete within 45 minutes. Contents were stirred at 40°C. for 6 hours after completing the addition. The progress of thereaction was monitored by gas chromatography (GC). GC analysis of analiquot revealed that the reaction was progressing slowly after 6 hoursat 40° C. The internal temperature was increased to 45° C. and thecontinued presence of1-[2-(3{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane wasobserved. Additional catalyst (0.25 mg) was added and the internaltemperature was increased further to 55° C. The reaction mixture wasstirred at 55° C. for 24 hours. The remaining amount of1-[2-(3{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane, asdetermined by GC analysis, had diminished to about 2% of it originalquantity. Further addition of catalyst (0.25 mg) did not improve thereaction conversion. The reaction mixture was diluted with 50 ml hexanesat ambient temperature and treated with charcoal. Charcoal was removedby filtration, and volatiles were removed by rotatory evaporator.Monofunctional epoxy monomer was then stirred under high vacuum (50-75millitorr) for 6 hours to remove remaining residual volatiles and theproduct was further purified by vacuum distillation. The final productwas collected in the temperature range of 145-150° C. (50 millitorr).The product, 3-(2-{1,1,3,3-tetramethyl-3-[2-(1,1,3,3-tetrame3-vinyl-disiloxanyl)-ethyl]-disiloxanyl}-ethyl)-7-oxa-bicyclo[4.1.0]heptane,was free from1-[2-(3{7-oxabicyclo[4.1.0]heptyl})ethyl]-tetramethyldisiloxane. Yieldwas 18.09 g, 76%.

EXAMPLE 5 Synthesis of the Compound Represented by Structural Formula(XXX)

[0096]

[0097] Tetrakis(dimethylsiloxy)silane (1.66 g, 5.0 mmol) and toluene (12ml) were charged into an oven dried 100 ml three-necked round-bottomflask equipped with a magnetic stirrer, a pressure equalized additionfunnel, thermometer, and an air condenser with a top mountedinlet/outlet for supply of inert gas. The mixture was stirred underinert gas atmosphere and then tetrakis(triphenylphosphine)platinum(0)(1.00 mg dissolved in 1.00 ml toluene) was added via a gas tight syringeat ambient temperature. Internal temperature was raised to 45° C.3-(2-{1,1,3,3-Tetramethyl-3-[2-(1,1,3,3-tetramethyl-3-vinyl-disiloxanyl)-ethyl]-disiloxanyl}-ethyl)-7-oxa-bicyclo[4.1.0]heptane(9.07 g, 20.4 mmol) and toluene (8 ml) were charged to the pressureequalized addition funnel and then added dropwise into the reactionvessel. Addition was complete within one hour and the reaction mixturewas stirred for an additional 6 hours. Infrared Spectroscopy (FTIR)analysis revealed remaining Si—H. Additional catalyst (0.25 mg) andmonovinyl precursor (0.35 g, 0.79 mmol) were added into the reactionflask at 45° C. The internal temperature was raised to 65° C. Thecontents were stirred at this temperature for 18 hours. InfraredSpectroscopy (FTIR) analysis revealed no remaining Si—H. The reactionmixture was cooled to ambient temperature and it was further dilutedwith 100 ml hexanes and treated with charcoal. Charcoal was removed byfiltration and volatiles were removed by rotatory evaporator.Tetrafunctional epoxy monomer was then stirred under high vacuum (50-75millitorr) for 6 hours to remove remaining residual volatiles, followedby filtration under nitrogen through a 1.0 μm syringe filter. Yield was9.8 g, 91%.

[0098] Photo-Differential Scanning Calorimetry (PDSC) was performed asdescribed in Example 1. Development of exothermicity was extremely rapidafter the onset of exposure to broad band Hg radiation at an irradiancelevel of 8.5 mW/cm². The peak position was at 0.130 minutes and theonset of exothermicity was at 0.064 minutes. The calculated enthalpy ofpolymerization reaction was 87.59 kJ/(mole epoxide equivalent).

EXAMPLE 6 Preparation of A Holographic Recording Medium with theCompound Prepared in Example 1

[0099] The polyfunctional monomer prepared in Example 1 was first addedto a difunctional epoxide monomer represented by Structural Formula(XIV):

[0100] where each group R⁵ is a 2-(3,4-epoxycyclohexyl)ethyl grouping;and each grouping R¹ is a methyl group, and which is available fromPolyset Corporation, Inc., Mechanicsville, N.Y., under the tradenamePC-1000. The mole ratio of polyfunctional monomer to difunctionalmonomer was 0.37:1.0. The mixture of monomers was then stirred to form auniform and homogeneous mixture. To this mixture was then added DOWCorning 705 silicone fluid in a mole ratio of 0.519:1.0 binder to totalmonomer, and the contents was then stirred at room temperature to form auniform mixture. To this mixture was added 6% by weight of the finalrecording medium of cumyltolyliodonium tetrakis(pentafluorophenyl)boratedissolved in methylene chloride, and the resulting mixture was stirredto form a uniform mixture. To this solution was added the sensitizer,5,12-bis(phenylethynyl)naphthacene, dissolved in methylene chloride at0.013% by weight of the final recording medium while stirring. Solventwas removed by bubbling with flowing argon and by application of vacuum.

[0101] Slant fringe, plane-wave, transmission holograms were recorded inthe above media in the conventional manner with two spatially filteredand collimated argon ion laser writing beams at 514.5 nm with equalirradiance levels directed onto the sample with equal semiangles ofabout 25° about the normal. A beam expanded and collimated HeNe probebeam, incident at the appropriate Bragg angle, was used to detect thedevelopment of holographic activity during exposure. Real timediffraction intensity data was obtained using two Model 818-SLphotodiodes and a dual channel multi-function optical meter Model 2835-Cfrom Newport Corporation. Six hundred plane-wave transmission hologramswere multiplexed sequentially and co-locationally using a scheduledexposure series combining angle and peristrophic multiplexing methods.The cumulative grating strength attained was measured from the sum ofthe square roots of the diffraction efficiencies for each individualhologram. The value exhibited by the medium with 200 micron thickness isabout 16.5. This value represents about a 40% improvement in dynamicrange as compared to results obtained for multiplexed recording carriedout in a similar fashion for recording media described in U.S. Pat. No.5,759,721 and in U.S. patent application No. 08-970,066. The finalphysical state of the fully exposed recording medium is more resistantto mechanical failure resulting from brittle mechanical propertiesassociated with crosslinked microstructure. Photodifferential scanningcalorimetry experiments, using Ar⁺ laser radiation at the same intensityas used for holographic recording, was carried out to measure the extentof polymerization reaction (kJ/mole epoxide) attained. The extent ofreaction achieved when the medium of the present invention was exposedto a level of saturation fluence was 74 kJ/mole epoxide, whichsubstantially exceeded the value exhibited by media described in U.S.Pat. No. 5,759,721 and in U.S. patent application No. 08-970,066.

EXAMPLE 7 Preparation of A Holographic Recording Medium with theCompound Prepared in Example 2

[0102] A polyfunctional monomer prepared in Example 2, with epoxyequivalent weight of 451 (grams/mole epoxide), was first added to adifunctional epoxide monomer of the Structural Formula (XIV) where eachgroup R⁵ is a 2-(3,4-epoxycyclohexyl)ethyl grouping; each grouping R¹ isa methyl group, and which is available from Polyset Corporation, Inc.,Mechanicsville, N.Y., under the tradename PC-1000. The mole ratio ofpolyfunctional monomer to difunctional monomer was 0.30:1.0. The mixtureof monomers was then stirred to form a uniform and homogeneous mixture.To this mixture was then added DOW Coming 705 silicone fluid in a moleratio of 0.664:1.0 binder to total monomer, and the contents was thenstirred at room temperature to form a uniform mixture. To this mixturewas added 6% by weight of the final recording medium ofcumyltolyliodonium tetrakis(pentafluorophenyl)borate dissolved inmethylene chloride, and the resulting mixture was stirred to form auniform mixture. To this solution was added the sensitizer,5,12-bis(phenylethynyl)naphthacene, dissolved in methylene chloride atabout 0.013 % by weight of the final recording medium while stirring.Solvent was removed by bubbling with flowing argon and by application ofmoderate vacuum.

[0103] Slant fringe, plane-wave, transmission holograms were recorded inthe above media in the conventional manner with two spatially filteredand collimated argon ion laser writing beams at 514.5 nm with equalirradiance levels directed onto the sample with equal semiangles ofabout 25° about the normal. A beam expanded and collimated HeNe probebeam, incident at the appropriate Bragg angle, was used to detect thedevelopment of holographic activity during exposure. Real timediffraction intensity data was obtained using two Model 818-SLphotodiodes and a dual channel multi-function optical meter Model 2835-Cfrom Newport Corporation. Six hundred plane-wave transmission hologramswere multiplexed sequentially and co-locationally using a scheduledexposure series combining angle and peristrophic multiplexing methods.The cumulative grating strength attained was measured from the sum ofthe square roots of the diffraction efficiencies for each individualhologram. The value exhibited by the medium with 200 micron thickness isabout 18. This value represents about a 50% improvement in dynamic rangeas compared to results obtained for multiplexed recording carried out ina similar fashion for recording media described in U.S. Pat. No.5,759,721 and in U.S. patent application No. 08-970,066.Photodifferential scanning calorimetry experiments, using Ar⁺ laserradiation at the same intensity as used for holographic recording, wascarried out to measure the extent of polymerization reaction (kJ/moleepoxide) attained. The extent of reaction achieved when the medium ofthe present invention was exposed to a level of saturation fluence, was78 KJ/mole epoxide, which substantially exceeded the value exhibited bymedia described in U.S. Pat. No. 5,759,721 and in U.S. patentapplication No. 08-970,066.

[0104] The shift in Bragg angle from the recording condition wasmeasured for the entire set of multiplexed plane-wave holograms thatwere recorded sequentially and co-locationally in the medium of thepresent invention. When the multiplexed recording was preceded byvarious pre-imaging exposure conditions, then values for both thedynamic range and the angular shifts were reduced from those observedwith no pre-imaging exposure. The magnitude of the shift in Bragg angleis directly related to the magnitude of transverse shrinkage ordimensional change in the thickness direction of the recording media,while the dynamic range is a measure of the materials storage capacity.Additionally, the measured angle shifts exhibited significantlydiminished values relative to those shown by recording media describedin U.S. Pat. No. 5,759,721 and in U.S. patent application No.08-970,066, whereas the cumulative grating strength attained by therecording medium of this invention exceeded the value exhibited byrecording media described in U.S. Pat. No. 5,759,721 and in U.S. patentapplication No. 08-970,066. Accordingly, the recording medium of thepresent invention exhibits both higher dynamic range and lower shrinkagethan observed for recording media such as described in U.S. Pat. No.5,759,721 and in U.S. patent application No. 08-970,066. The finalphysical state of the fully exposed recording medium is more resistantto mechanical failure resulting from brittle mechanical propertiesassociated with crosslinked microstructure.

EXAMPLE 8 Polyfunctional Monomers Suitable For Use in HolographicRecording Materials

[0105] Shown below are the structures of other polyfunctional monomersprepared by the synthetic methods described herein and shown to besuitable according to methods in Examples 6 and 7 for use in holographicrecording materials:

[0106] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A compound represented by the followingstructural formula:

wherein: each group R⁷ is an unsubstituted aliphatic group, asubstituted aliphatic group, an unsubstituted aryl group, a substitutedaryl group; each group R⁸ is R⁹, hydrogen, an alkenyl, a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substitutedC₁₋₁₂-alkyl or aryl or R^(z)—(O—Y₁)_(m)—,(R^(z))₃Si—(O—Si(R^(z))₂)_(q)—Y₁— or (R^(z))₃Si—(O—Si(R^(z))₂)_(q)—O—;each R⁹ is independently represented by the following structuralformula:

wherein: X₁ and X₂ are independently an inert linking group; each R^(a)is independently a substituted or unsubstituted aliphatic group or asubstituted or unsubstituted aryl group; each R^(b) is an aliphaticgroup substituted with an epoxide; each R^(z) is independently asubstituted or unsubstituted C₁₋₁₂ alkyl group, C₁₋₁₂ cycloalkylalkylgroup, aryl substituted C₁₋₁₂ alkyl group or aryl group; each Y₁ isindependently a C₁₋₁₂ alkylene group; m is an integer from 1 to 10; andq is an integer from 0 to
 4. 2. The compound of claim 1 wherein: each R⁷is independently a substituted or unsubstituted C₁₋₁₂ alkyl, C₁₋₁₂cycloalkyl, aryl substituted C₁₋₁₂ alkyl or aryl group; each R⁹ isrepresented by

each group R¹⁰ is independently a substituted or unsubstituted C₁₋₁₂alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylene group,—Y₁—[O—Y₁]_(p)—, —Y₁—Si(R^(z))₂—Y₁—,—Y₁—Si(R^(z))₂—Y₁—O—Y₁—Si(R^(z))₂—Y₁—, or—Y₁—Si(R^(z))₂—Y₁—Si(R^(z))₂—Y₁—; each R^(z) is independently a C₁₋₁₂alkyl group; each Y₁ is independently a C₁₋₁₂ alkylene group; each groupR¹¹ and R¹² is independently a substituted or unsubstituted C₁₋₁₂ alkyl,C₁₋₁₂ cycloalkyl, aryl substituted C₁₋₁₂ alkyl group or aryl group; andeach group R¹³ is independently an epoxide substituted aliphatic grouphaving from 2-10 carbon atoms.
 3. The compound of claim 2 wherein: R⁸ issubstituted or unsubstituted C₁₋₁₂ alkylsilane, C₁₋₁₂ cycloalkylsilane,C₁₋₁₂ alkoxysilane, arylsubstituted C₁₋₁₂ alkyl silane or a substitutedor unsubstituted 1-alkenyl group or a substituted or unsubstituted C₁₋₁₂n-alkenyl group where n is greater than or equal to 1; R¹⁰ isindependently a C₁₋₁₂ alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene,or arylene group.
 4. The compound of claim 3 wherein at least one groupR¹³ comprises a cycloalkene oxide.
 5. The compound of claim 4 whereineach R¹³ is represented by the following structural formula:


6. The compound of claim 3 wherein: R⁷ is a methyl group, R⁸ is ethenylor R⁹; each R⁹ is

each group R¹⁰ is —(CH₂)₂—, —(CH₂)₆— or —(CH₂)₈—; each group R¹¹ and R¹²are a methyl group; and each group R¹³ is a 2-(3,4-epoxycyclohexyl)ethyl group.
 7. A holographic recording medium comprising: a) at leastone polyfunctional epoxide monomer or oligomer represented by thefollowing structural formula:

wherein: each group R⁷ is an unsubstituted aliphatic group, asubstituted aliphatic group, an unsubstituted aryl group, a substitutedaryl group; each group R⁸ is R⁹, hydrogen, an alkenyl, a substituted orunsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, aryl substitutedC₁₋₁₂-alkyl or aryl or R^(z)—(O—Y₁)_(m)—,(R^(z))₃Si—(O—Si(R^(z))₂)_(q)—Y₁— or (R^(z))₃Si—(O—Si(R^(z))₂)_(q)—O—;each R⁹ is independently represented by the following structuralformula:

wherein: X₁ and X₂ are independently an inert linking group; each R^(a)is independently a substituted or unsubstituted aliphatic group or asubstituted or unsubstituted aryl group; each R^(b) is an aliphaticgroup substituted with an epoxide; each R^(z) is independently asubstituted or unsubstituted C₁₋₁₂ alkyl group, C₁₋₁₂ cycloalkylalkylgroup, aryl substituted C₁₋₁₂ alkyl group or aryl group; each Y₁ isindependently a C₁₋₁₂ alkylene group; m is an integer from 1 to 10; andq is an integer from 0 to 4, and wherein each monomer or oligomer has anepoxy equivalent weight of greater than about 300 g/mole epoxide; a) abinder which is capable of supporting cationic polymerization; b) anacid generator capable of producing an acid upon exposure to actinicradiation; and optionally c) a sensitizer.
 8. The holographic recordingmedium of claim 7, additionally comprising a difunctional epoxidemonomer.
 9. The holographic recording medium of claim 7, additionallycomprising a monofunctional epoxide monomer.
 10. The holographicrecording medium of claim 7 wherein: each R⁷ is independently asubstituted or unsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, arylsubstituted C₁₋₁₂ alkyl or aryl group; each R⁹ is represented by

each group R¹⁰ is independently a substituted or unsubstituted C₁₋₁₂alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂ arylalkylene, or arylene group,—Y₁—[O—Y₁]_(p)—, —Y₁—Si(R^(z))₂—Y₁—,—Y₁—Si(R^(z))2—Y₁—O—Y₁—Si(R^(z))₂—Y₁—, or—Y₁—Si(R^(z))₂—Y₁—Si(R^(z))₂—Y₁—; each R^(z) is independently a C₁₋₁₂alkyl group; each Y₁ is independently a C₁₋₁₂ alkylene group; p is aninteger from 1 to 5; each group R¹¹ and R¹² is independently asubstituted or unsubstituted C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, arylsubstituted C₁₋₁₂ alkyl group or aryl group; and each group R¹³ isindependently an epoxide substituted aliphatic group having from 2-10carbon atoms.
 11. The holographic recording medium of claim 10 wherein:R⁸ is substituted or unsubstituted C₁₋₁₂ alkylsilane, C₁₋₁₂cycloalkylsilane, C₁₋₁₂ alkoxysilane, arylsubstituted C₁₋₁₂ alkyl silaneor a substituted or unsubstituted 1-alkenyl group or a substituted orunsubstituted C₁₋₁₂ n-alkenyl group where n is greater than or equal to1; R¹⁰ is independently a C₁₋₁₂ alkylene, C₁₋₁₂ cycloalkylene, C₁₋₁₂arylalkylene, or arylene group.
 12. The holographic recording medium ofclaim 11 wherein at least one group R¹³ comprises a cycloalkene oxide.13. The holographic recording medium of claim 12 wherein each R¹³ isrepresented by the following structural formula:


14. The holographic recording medium of claim 13 wherein: R⁷ is a methylgroup, R⁸ is -ethenyl or R⁹; each R⁹ is

each group R¹⁰ is —(CH₂)₂—, —(CH₂)₆— or —(CH₂)₈—; each group R¹¹ and R¹²are a methyl group; and each group R¹³ is a 2-(3,4-epoxycyclohexyl)ethyl group.
 15. The holographic recording medium of claim 8 wherein thedifunctional epoxide monomer is represented by the following structuralformula: R²⁴Si(R²⁵)₂OSi(R²⁶)₂R²⁴ where each group R²⁴ is a2-(3,4-epoxycyclohexyl)ethyl grouping; each grouping R²⁵ is a methylgroup, and each group R²⁶ is a methyl group.
 16. The holographicrecording medium of claim 8 wherein the holographic medium comprisesbetween about 0.25 to about 5 parts by weight of the difunctionalepoxide monomer per part by weight of the polyfunctional epoxidemonomer.
 17. The holographic recording medium of claim 7 wherein theholographic medium comprises from about 90 parts binder and 10 partsmonomer or oligomer (w/w) to about 10 parts binder and 90 parts monomeror oligomer (w/w).
 18. The holographic recording medium of claim 7wherein the acid generator capable of producing an acid upon exposure toactinic radiation is a diaryliodonium salt.
 19. A holographic recordingmedium of claim 7 wherein the sensitizer is5,12-bis(phenylethynyl)naphthacene.